The word plastics is from the Greek word

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The word plastics is from the Greek word Plastikos, meaning “able to be shaped

The word plastics is from the Greek word Plastikos, meaning “able to be shaped and molded” Ken Youssefi Mechanical Engineering 1

Why Design with Plastics? • Light weight, high weight to strength ratio, particularly when

Why Design with Plastics? • Light weight, high weight to strength ratio, particularly when reinforced • Relatively low cost compared to metals and composites Density Ken Youssefi Cost Mechanical Engineering 2

Why Design with Plastics? • Corrosion resistance • Low electrical and thermal conductivity, insulator

Why Design with Plastics? • Corrosion resistance • Low electrical and thermal conductivity, insulator • Easily formed into complex shapes, can be formed, casted and joined. • Wide choice of appearance, colors and transparencies Ken Youssefi Mechanical Engineering 3

Disadvantages of using Plastics • Low strength o • Low useful temperature range (up

Disadvantages of using Plastics • Low strength o • Low useful temperature range (up to 600 F) • Less dimensional stability over period of time (creep effect) • Aging effect, hardens and become brittle over time • Sensitive to environment, moisture and chemicals • Poor machinability Ken Youssefi Mechanical Engineering 4

Ken Youssefi Mechanical Engineering 5

Ken Youssefi Mechanical Engineering 5

Mechanical Properties of Various Plastics Brass: 200 to 850 MPa Steel: 350 to 1900

Mechanical Properties of Various Plastics Brass: 200 to 850 MPa Steel: 350 to 1900 MPa Aluminum: 100 to 550 MPa Ken Youssefi Mechanical Engineering 6

Polymers • The earliest synthetic polymer was developed in 1906, called Bakelite. • The

Polymers • The earliest synthetic polymer was developed in 1906, called Bakelite. • The development of modern plastics started in 1920 s using raw material extracted from coal and petroleum products (Ethylene). Ethylene is called a building block. • Polymers are long-chain molecules and are formed by polymerization process, linking and cross linking a particular building block (monomer, a unit cell). • The term polymer means many units repeated many times in a chainlike structure. • Most monomers are organic materials, atoms are joined in covalent bonds (electron-sharing) with other atoms such as oxygen, nitrogen, hydrogen, sulfur, chlorine, …. Ken Youssefi Mechanical Engineering 7

The structure of polymers Ken Youssefi Mechanical Engineering 8

The structure of polymers Ken Youssefi Mechanical Engineering 8

Classification of polymers There are two major classifications of polymers Thermoplastics As the temperature

Classification of polymers There are two major classifications of polymers Thermoplastics As the temperature is raised above the melting point, the secondary bonds weaken, making it easier to form the plastic into any desired shape. When polymer is cooled, it returns to its original strength and hardness. The process is reversible. Polymers that show this behavior are known as thermoplastics. Thermosetting Plastics (thermosets) Thermosetting plastics are cured into permanent shape. Cannot be re-melted to the flowable state that existed before curing, continued heating for a long time leads to degradation or decomposition. This curing (cross-linked) reaction is irreversible. Thermosets generally have better mechanical, thermal and chemical properties. They also have better electrical resistance and dimensional stability than do thermoplastics. Ken Youssefi Mechanical Engineering 9

Polymer’s Structures Bonding – monomers are linked together by covalent bonds, forming a polymer

Polymer’s Structures Bonding – monomers are linked together by covalent bonds, forming a polymer chain (primary bonds). The polymer chains are held together by secondary bonds. The strength of polymers comes in part from the length of polymer chains. The longer the chain, the stronger the polymer. More energy is needed to overcome the secondary bonds. Linear polymers A sequential structure resulting in thermoplastics like nylon, acrylic, polyethylene. A linear polymer may contain some branched and cross-linked chains resulting in change in properties. Ken Youssefi Branched polymers Side branch chains are attached to the main chain which interferes with the relative movement of the molecular chains. This results in an increase in strength, deformation resistance and stress cracking resistance. Lower density than linear chain polymers. Mechanical Engineering 10

Polymer’s Structures Cross-linked polymers Three dimensional structure, adjacent chains are linked by covalent bonds.

Polymer’s Structures Cross-linked polymers Three dimensional structure, adjacent chains are linked by covalent bonds. Polymers with cross-linked chains are called thermosetting plastics (thermosets), epoxy and Silicones. Cross-linking is responsible for providing hardness, strength, brittleness and better dimensional stability. Network polymers A three dimensional network of three or more covalent bonds. Thermoplastic polymers that have been already formed could be cross-linked to obtain higher strength. Polymers are exposed to high-energy radiation. Ken Youssefi Mechanical Engineering 11

Additives in Plastics Additives are added to polymers in order to obtain or improve

Additives in Plastics Additives are added to polymers in order to obtain or improve certain properties such as strength, stiffness, color, resistance to weather and flammability. Plasticizers are added to obtain flexibility and softness, most common use of plasticizers are in PVC. Ultraviolet radiation (sunlight) and oxygen cause polymers to become stiff and brittle, they weaken and break the primary bonds. A typical treatment is to add carbon black (soot) to the polymer, it absorbs radiation. Antioxidants are also added to protect against degradation. Fillers such as fine saw dust, silica flour, calcium carbide are added to reduce the cost and to increase harness, strength, toughness, dimensional stability, …. . Ken Youssefi Mechanical Engineering 12

Additives in Plastics • Colorants are added to obtain a variety of colors. Colorants

Additives in Plastics • Colorants are added to obtain a variety of colors. Colorants are either organic (dye) or inorganic (pigments). Pigments provide greater resistance to temperature and sunlight. • Flame retardants such as chlorine, phosphorus and bromine, are added to reduce polymer flammability. Teflon does not burn and nylon and vinyl chloride are self-extinguishing. • Lubricants such as mineral oil and waxes are added to reduce friction. Ken Youssefi Mechanical Engineering 13

Applications of Thermoplastics Design requirement: strength Applications: Valves, gears, cams, pistons, fan blades, …

Applications of Thermoplastics Design requirement: strength Applications: Valves, gears, cams, pistons, fan blades, … Plastics: nylon, acetal (delrin), polycarbonate, phenolic Design requirement: wear resistance Applications: bearings, gears, bushings, wheels, …. Plastics: nylon, acetal (delrin), polyurethane, phenolic, polymide Ken Youssefi Mechanical Engineering 14

Applications of Thermoplastics Design requirement: functional and decorative Applications: knobs, handles, cases, moldings, pipe

Applications of Thermoplastics Design requirement: functional and decorative Applications: knobs, handles, cases, moldings, pipe fittings, … Plastics: ABS, acrylic, polyethylene, phenolic, polypropylene, polystyrene Design requirement: functional and transparent Applications: lens, goggles, signs, food processing equipment, … Plastics: acrylic, polycarbonate, polystyrene, polysulfone Design requirement: hollow shapes and housings Applications: pumps, helmets, power tools, cases, … Plastics: ABS, polyethylene, phenolic, polypropylene, polystyrene, polycarbonate Ken Youssefi Mechanical Engineering 15

Popular Plastics Polyethylene (LDPE (low density) and HDPE (high density) Properties: good chemical and

Popular Plastics Polyethylene (LDPE (low density) and HDPE (high density) Properties: good chemical and electrical properties, strength depends on composition Applications: bottles, garbage cans, housewares, bumpers, toys, luggage Acetal (Delrin) Properties: good strength, good stiffness, good resistance to heat, moisture, abrasion and chemicals Applications: mechanical components; gears, bearings, valves, rollers, bushings, housings ABS Properties: dimensionally stable, good strength, impact and toughness properties, good resistance to abrasion and chemicals Applications: automotive components, helmets, tool handles, appliances, boat hulls, luggage, decorative panels Ken Youssefi Mechanical Engineering 16

Popular Plastics Polycarbonates Properties: very versatile and has dimensional stability, good mechanical and electrical

Popular Plastics Polycarbonates Properties: very versatile and has dimensional stability, good mechanical and electrical properties, high resistance to impact and chemicals Applications: optical lenses, food processing equipments, electrical components and insulators, medical equipments, windshields, signs, machine components Nylons Properties: good mechanical and abrasion resistance property, selflubricating, resistant to most chemicals but it absorbs water, increase in dimension is undesirable Applications: mechanical components; gears, bearings, rollers, bushings, fasteners, guides, zippers, surgical equipments, Ken Youssefi Mechanical Engineering 17

Applications of Thermosetting Plastics Epoxies Properties: good dimensional stability, excellent mechanical and electrical properties,

Applications of Thermosetting Plastics Epoxies Properties: good dimensional stability, excellent mechanical and electrical properties, good resistance to heat and chemicals Applications: electrical components requiring strength, tools and dies, fiber reinforced epoxies are used in structural components, tanks, pressure vessels, rocket motor casing Phenolics Properties: good dimensional stability, rigid, high resistance to heat, water, electricity, and chemicals Applications: laminated panels, handles, knobs, electrical components; connectors, insulators Ken Youssefi Mechanical Engineering 18

Applications of Thermosetting Plastics Polyesters (thermosetting, reinforced with glass fibers) Properties: good mechanical, electrical,

Applications of Thermosetting Plastics Polyesters (thermosetting, reinforced with glass fibers) Properties: good mechanical, electrical, and chemical properties, good resistance to heat and chemicals Applications: boats, luggage, swimming pools, automotive bodies, chairs Silicones Properties: excellent electrical properties over a wide rang of temperature and humidity, good heat and chemical properties Applications: electrical components requiring strength at high temp. , waterproof materials, heat seals Ken Youssefi Mechanical Engineering 19

Website: www. ge. com/plastics Plastics Stress vs. Strain curve Ken Youssefi Mechanical Engineering 20

Website: www. ge. com/plastics Plastics Stress vs. Strain curve Ken Youssefi Mechanical Engineering 20

Structural and mechanical Appl. Light duty mechanical & decorative Gears, cams, pistons, rollers, fan

Structural and mechanical Appl. Light duty mechanical & decorative Gears, cams, pistons, rollers, fan Handles, knobs, steering wheel, blades, rotors, pump impellers, tool handles, pipe fittings, camera cases, eyeglass frames washing machine agitators ABS X Acetal (Delrin) X Acrylic X X Cellulosics Thermosets Thermoplastics Fluoroplastics Nylon Phenylene Oxide Polycarbonate Polyester Polyethylene Polyimide Polyenylene sulfide Polypropylene Polystyrene Polysulfone Polyurethane Polyvinyl chloride Phenolic Polyester Polyurethane Ken Youssefi X X X X Mechanical Engineering 21

Parts for wear applications Gears, bearings, bushings, tracks, wheels, ware strips Thermosets Thermoplastics ABS

Parts for wear applications Gears, bearings, bushings, tracks, wheels, ware strips Thermosets Thermoplastics ABS Acetal (Delrin) Acrylic Cellulosics Fluoroplastics Nylon Phenylene Oxide Polycarbonate Polyester Polyethylene Polyimide Polyenylene sulfide Polypropylene Polystyrene Polysulfone Polyurethane Polyvinyl chloride Phenolic Polyester Polyurethane Ken Youssefi X Optical and transparent parts Lenses, safety glasses, signs, refrigerator shelves, windshields X X X X Mechanical Engineering 22

Small housing & hollow shapes Phone and flashlight cases, helmets, housings for power tools,

Small housing & hollow shapes Phone and flashlight cases, helmets, housings for power tools, pumps, small appliances X Thermosets Thermoplastics ABS Acetal (Delrin) Acrylic Cellulosics Fluoroplastics Nylon Phenylene Oxide Polycarbonate Polyester Polyethylene Polyimide Polyenylene sulfide Polypropylene Polystyrene Polysulfone Polyurethane Polyvinyl chloride Phenolic Polyester Polyurethane Ken Youssefi Large housing & hollow shapes Boat hulls, large appliance housings, tanks, tubs, ducts, refrigerator liners X X X X X Mechanical Engineering 23

Thermosets Thermoplastics Plastic Ken Youssefi Structural & Light Mechanical duty mech & deco ABS

Thermosets Thermoplastics Plastic Ken Youssefi Structural & Light Mechanical duty mech & deco ABS Acetal (Delrin) X Acrylic Cellulosics Fluoroplastics X Nylon Phenylene Oxide Polycarbonate Polyester Polyethylene Polyimide Polyenylene sulfide X Polypropylene Polystyrene Polysulfone Polyurethane Polyvinyl chloride X Phenolic Polyester Polyurethane X X Small housing & hollow shapes X Large Parts for Optical and housing wear transparent & hollow applications parts shapes X X X X X X X X X Mechanical Engineering X X 24

Manufacturing Processes for Plastics Fabrication of Plastics Injection Molding Ejector pin Molded part Heaters

Manufacturing Processes for Plastics Fabrication of Plastics Injection Molding Ejector pin Molded part Heaters Granular plastic Plunger Torpedo Ken Youssefi Mechanical Engineering 25

Ken Youssefi Mechanical Engineering 26

Ken Youssefi Mechanical Engineering 26

DFM Design Guidelines Injection Molding Provide adequate draft angle for easier mold removal. Minimize

DFM Design Guidelines Injection Molding Provide adequate draft angle for easier mold removal. Minimize section thickness, cooling time is proportional to the square of the thickness, reduce cost by reducing the cooling time. Ken Youssefi Mechanical Engineering 27

DFM Design Guidelines Injection Molding Keep rib thickness less than 60% of the part

DFM Design Guidelines Injection Molding Keep rib thickness less than 60% of the part thickness in order to prevent voids and sinks. Ken Youssefi Avoid sharp corners, they produce high stress and obstruct material flow. Mechanical Engineering 28

DFM Design Guidelines Injection Molding Provide smooth transition, avoid changes in thickness when possible.

DFM Design Guidelines Injection Molding Provide smooth transition, avoid changes in thickness when possible. Ken Youssefi Keep section thickness uniform around bosses. Mechanical Engineering 29

DFM Design Guidelines Injection Molding • Use standard general tolerances, do not tolerance; Dimension

DFM Design Guidelines Injection Molding • Use standard general tolerances, do not tolerance; Dimension Tolerance 0 ≤ d ≤ 25 ± 0. 5 mm 0 ≤ d ≤ 1. 0 ± 0. 02 inch 25 ≤ d ≤ 125 ± 0. 8 mm 1 ≤ d ≤ 5. 0 ± 0. 03 inch 125 ≤ d ≤ 300 ± 1. 0 mm 5 ≤ d ≤ 12. 0 ± 0. 04 inch 300 ± 1. 5 mm 12. 0 ± 0. 05 inch • Minimum thickness recommended; . 025 inch or. 65 mm, up to. 125 for large parts. • Round interior and exterior corners to. 01 -. 015 in radius (min. ), prevents an edge from chipping. Ken Youssefi Mechanical Engineering Standard thickness variation. 30

Rotational Molding Rotational molding process consists of six steps • A predetermined amount of

Rotational Molding Rotational molding process consists of six steps • A predetermined amount of plastic, powder or liquid form, is deposited in one half of a mold. • The mold is closed. • The mold is rotated biaxially inside an oven. • The plastics melts and forms a coating over the inside surface of the mold. • The mold is removed from the oven and cooled. • The part is removed from the mold. Ken Youssefi Mechanical Engineering 31

Rotational Molding Machines Vertical wheel machine Turret machine Shuttle machine Ken Youssefi Rock and

Rotational Molding Machines Vertical wheel machine Turret machine Shuttle machine Ken Youssefi Rock and roll machine Mechanical Engineering 32

Rotational Molding Advantages Ken Youssefi • Molds are relatively inexpensive. • Rotational molding machines

Rotational Molding Advantages Ken Youssefi • Molds are relatively inexpensive. • Rotational molding machines are much less expensive than other type of plastic processing equipment. • Different parts can be molded at the same time. • Very large hollow parts can be made. • Parts are stress free. • Very little scrap is produced Mechanical Engineering 33

Rotational Molding Limitations • Can not make parts with tight tolerance. • Large flat

Rotational Molding Limitations • Can not make parts with tight tolerance. • Large flat surfaces are difficult to achieve. • Molding cycles are long (10 -20 min. ) Materials Polyethylene (most common), Polycarbonate (high heat resistance and good impact strength), Nylon (good wear and abrasion resistance, good chemical resistance, good toughness and stiffness). Ken Youssefi Mechanical Engineering 34

Rotational Molding Nominal wall thickness • Polycarbonate wall thickness is typically between. 06 to.

Rotational Molding Nominal wall thickness • Polycarbonate wall thickness is typically between. 06 to. 375 inches, . 125 inch being an ideal thickness. • Polyethylene wall thickness is in the range of. 125 to. 25 inch, up to 1 inch thick wall is possible. • Nylon wall thickness is in the range of. 06 to. 75 inch. Ken Youssefi Mechanical Engineering 35

Rotational Molding Examples Ken Youssefi Mechanical Engineering 36

Rotational Molding Examples Ken Youssefi Mechanical Engineering 36

Rotational Molding Examples Ken Youssefi Mechanical Engineering 37

Rotational Molding Examples Ken Youssefi Mechanical Engineering 37

Blow Molding Blow molding is generally the same process as glass blowing adapted to

Blow Molding Blow molding is generally the same process as glass blowing adapted to polymers. In extrusion blow molding a tube is extruded and clamped in a split mold. Air under pressure (50 -100 psi) is injected into the tube blowing the plastic outward to fill the mold cavity. Ken Youssefi Mechanical Engineering 38

Blow Molding • Blow molding is used for medium size, hollow thin-walled shapes; containers,

Blow Molding • Blow molding is used for medium size, hollow thin-walled shapes; containers, tool cases, hollow structures, …. • Blow molding is limited to thermoplastics such as polyethylene, polycarbonate, ABS. • Wall thickness between. 015 -. 125 • Maximum tolerance. 01 -. 04 Ken Youssefi Mechanical Engineering 39